1. Field of the Invention
The invention relates generally to continuous passenger conveyor systems, such as escalators and moving walks, and, more particularly, to a method and apparatus for preventing passenger entrapment and providing lateral guidance to the moving assembly of the passenger conveyor.
2. Prior Art
Until the present invention, in all escalator systems, a running clearance gap has necessarily been provided between each of the lateral edges of the moving stairs and the adjacent, stationary, balustrade skirt panel in order to prevent the two from contacting each other. Consequently, various objects may intrude into this open gap and objects having a high coefficient of friction, e.g., passenger body extremities such as fingers and toes, or passenger apparel such as wet or dry-soled foortwear, rubber overshoes, sneakers, wellies or loose clothing, when placed in frictional contact with one of the skirt panels, may be drawn into this gap by the skirt panel and entrapped therein. Thus, such high frictional objects extending from the top tread surface of an upwardly moving escalator step against an adjacent, stationary skirt panel may be drawn by the skirt panel into this open gap and entrapped between the step and the skirt panel. Similarly, such objects extending from the generally vertical riser surface of a downwardly moving escalator step against an adjacent stationary skirt panel may be drawn into this gap and entrapped therein. When this entrapment occurs along the incline plane of the step travel, the pinching, drawing and knurling action, exerted on the object by the step side and the skirt panel, usually cuts and mutilates the object. When this entrapment occurs in the proximity of the escalator comb plate, even more serious consequences may result. For example, if the entrapped object is the toe of a small child's sneaker and the escalator is not stopped before the sneaker comes into contact with the comb plate, it is likely that both the sneaker toe and the child's toes enclosed therein will be amputated by the comb plate. Similarly, the entrapped fingers of a small child are usually amputated by the comb plate.
Because of the inherent danger involved in having an open gap between escalator stairs and adjacent skirt panels, since 1942 the American National Standard Safety Code for Elevators, Dumbwaiters, Escalators and Moving Walks, ANSI A17.1, has prescribed limitations for this running clearance gap. The 1942 supplement of this safety code added the requirement for newly installed escalators that the clearance on either side of the steps between the step tread and adjacent skirt panel not exceed 3/16 inch. This requirement was made more stringent in the 1955 edition of this safety code, which stated that the clearance on either side not exceed 3/16 inch, and that the sum of the clearances on both sides of the steps not exceed 1/4 inch. This requirement was relaxed in the 1971 edition, which doubled the allowable running clearance on either side of the step treads and adjacent skirt panel from 3/16 inch to 3/8 inch, and deleted any reference to a limit of the sum of the clearances on both sides. This requirement was again made more stringent in a 1980 supplement to this code, which reinstated the original requirement that the clearance on either side of the step not exceed 3/16 inch. However, this 1980 code supplement did not reinstate the 1955 to 1971 code requirement that the sum of the clearances on both sides of the steps not exceed 1/4 inch. Thus, the changes which have been made in the code requirements concerning the maximum width of this running clearance gap over the past 40 years indicates the difficulty of maintaining a narrow running clearance between the step tread and adjacent skirt panels.
Regardless of present or past code requirements. it is well known by escalator manufacturers, insurance companies, elevator consultants, and litigants to accidents that high frictional and flexible objects, such as soft-soled shoewear, fingers, toes, etc., can still be drawn into, and entrapped, in a relatively narrow gap.
Due to the constant eccentric loading imposed on an escalator stairway in operation, and the consequent wear on the bearings, the sides of the track system and the wheels running therein, the lateral movement of the steps increases. Thus, on an escalator which has been in use for a period of years, a person standing on one of the escalator steps can cause the step to shift ffrom one side to the other merely by shifting his weight sideways, thus increase the normal running clearance of that step on one side. For this reason, it is doubtful that most of the estimated 30,000 escalators in operation at the present time in the United States can meet any of the maximum running clearance requirements of the American National Standard Safety Code, enacted since 1942, if accurately measured.
Also, since at least 1974, the American National Standard Safety Code began to require a "skirt obstruction device" be furnished on all new escalators. This device is defined in the code as means to cause the opening of the power circuit to the escalator driving machine motor and brake should an object between the step and the skirt panel as a step approaches the lower comb plate. Since at least 1978, this requirement has been extended to apply also to the upper comb plate. Typically, this skirt obstruction device comprises four safety switches, or sets of switches, which are mounted in the skirt panels at theupper and lower end thereof, respectively, at various distances (unspecified by code) from the comb plate, usually no more than two feet. Flexible objects having a high coefficient of friction, such as footwear of rubber material or toe or fingers of a person, which becomes wedged between the edge of the moving step (generally cast aluminum) and the stationary skirt panel (typically stainless steel or procelain enamel) will continue to be entrapped along the travel of the escalator between the switches, until and if the safety switch at either the top or botton of the escalator is actuated by a force or pressure exerted on it by the trapped object. Some escalators, especially older models, have microswitches for stopping the escalator located behind the flexible skirt panels. In such escalators, an object trapped between the step side and the skirt panel must create sufficient force or pressure to deflect the skirt panel outwardly in order to operate the microswitch located behind it. Such deflectible skirt panels compound the danger of these exposed running clearance gaps by allowing the clearance gap to become greater after an object is trapped therein and thus allows a larger portion of the object to be drawn inward. For this reason, the Canadian Safety Code has required for many years that, on newly installed escalators, skirt panels shall not deflect more than 0.06 inch under a force of 150 pounds at any exposed point between the upper and lower comb plates.
Since 1980, the American National Standard Safety Code has required a deflection of not more than 1/16 inch under a force of 150 pounds at any exposed point between the upper and lower comb plates.
Skirt panels manufactured in the United States prior to this 1980 restriction are capable of deflecting variable amounts depending on such design factors as the gauge thickness and Brinell hardness of the sheet metal outer layer of the skirt panel, the reinforcement, such as formed metal, plywood, or chipped board, the spacing between reinforcements, etc.
In more recent years and currently, skirt safety switches are mounted behind the skirt panels but have operating heads or buttons which extend through openings in the skirt panels and which are intended to be directly activated by respective entrapped objects passing thereby.
Such skirt safety switches, when properly adjusted, should detect any entrapped object passing over them and actuate the drive machine brake to stop the escalator. However, these skirt safety switches can be operated unnecessarily by lateral shifting of a step of an older escalator caused by a passenger standing on the step suddenly shifting his weight. Thus, there always exists the danger that a service or maintenance mechanic, in adjusting the location of these switches away from the running step sides in order to prevent such unnecessary shut-downs, renders the switch relatively inoperative when an entrapped object passes through the switch area.
Obviously, a skirt safety switch only performs its designated function if it stops the escalator before the entrapped object actuating this safety switch enters the comb plate. However, the stopping rate or distance of an escalator, which has never been specified by the American National Standard Code or Canadian Standards Association Code, varies considerably with the number of people riding the escalator, the direction of the escalator speed, the spring tension on the brake, the size of the brake shoes, lubrication of moving parts and so forth. For example, a fully loaded escalator when traveling in an upward direction may be able to stop after traveling only six inches after the skirt safety switch was actuated, whereas the same fully loaded escalator when traveling in the downward direction may travel as much as six feet after the skirt safety switch is activated before stopping. When the escalator is traveling in an upward direction, the weight of the passengers being lifted adds to the stopping force of the brake whereas when the escalator is traveling in a downward direction, the passenger weight will drive the machine through the brake and the steps will drift further before coming to rest.
Also, since an escalator operates at an angle of no more than 30.degree. from the horizontal in this country (and 35.degree. in some other countries), during an emergency stop of the escalator, the escalator passengers are subjected to a forward force. Therefore, the maximum deceleration rate of the escalator, which occurs when the escalator is carrying a minimum number of passengers, must not exceed a rate of approximately one foot per second squared, in order to prevent throwing the passengers forward during the stopping operation. Thus, there is a greater danger that an escalator cannot be stopped by a skirt safety switch before the entrapped object reaches the escalator comb plate when the escalator is fully loaded and moving in a downward direction.
The majority of entrapment accidents occurring on escalators generally involve young children. Obviously, it is more difficult for a parent to observe and control his or her child while travelling on a fully loaded escalator rather than a lightly loaded one. Thus, on a heavily loaded downward moving escalator, the maximum difficulty in a parent overseeing a child coincides with the maximum danger of serious injury to the child should the child's sneaker or fingers become wedged between the moving stair side and the stationary skirt panel. For this reason, entrapment accidents regularly occur on even new escalators at museums, exhibits, amusements parks, etc., which are frequently crowded on weekends and holidays, at which times a high percentage of the escalator passengers are children.
Also, in order to reduce entrapment of objects within the exposed running clearance gaps between the moving steps and the stationary skirt panel, since 1971 the American National Standards Safety Code has required that the skirt panel adjacent to the step be of a material having a smooth surface, and that embossed, perforated or roughly texture materials shall not be used for these skirt panels. While this reduces the coefficient of friction between an object inserted into this gap and the skirt panel which exerts the force on this object to pull it into the gap, it does not prevent high frictional, pliable objects, such as the rubber toe or heels of sneakers or overshoes, or the fingers or hand of a child, from being pulled inwardly into this gap by the skirt panel during operation of the escalator.
In addition to the code requirements discussed above, various methods and devices have been proposed for reducing the likelihood of entrapping an object in the exposed running clearance space between a moving escalator step and the adjacent stationary skirt panel, and some of these have been adapted by escalator manufacturers and incorporated into their escalator systems. For example, the Hitachi Company of Japan uses longitudinally grooved escalator step treads in which several of the tread strips at both sides of the step adjacent the skirt panel extend upward approximately 8 mm above the remainder of the tread strips, which are of uniform height, so that when the passenger places his foot close to the edge, he will feel this difference in elevation and move his foot more to the center. This step plate construction is described in the German Pat. No. 2,161,442, published July 13, 1972. The Hitachi Company also provides yellow demarcation lines on all four sides of the step tread to thus delineate areas of this tread which should be avoided by the passengers. Unfortunately, the largest class of escalator entrapment accidents involve the young children, for whom the brightly colored raised tread strips adjacent the skirt panel may serve as an attraction, rather than as a deterent.
Also, on some of the escalators manufactured by the Hitachi Company, the surface of the skirt panel is coated with polytetra fluoroethylene low-friction fluorocarbon resin commercially available under the trademark "Teflon", to reduce the friction between the skirt panel and a shoe pressing contact against it, to thus minimize the possibility that the shoe will be drawn into the operating clearance gap between the moving stair and the stationary skirt panel. The chief disadvantage of such a Teflon-coated skirt panel is that Teflon is a relatively soft material. Thus, it is imperative the sides of the escalator steps, which are generally cast aluminum material of rough texture, not come into contact wih the Teflon-coated skirt panel. Also, objects having rough surfaces or sharp edges, such as delivery hand trucks, or baggage hand carts, generally used in transportation terminals must not come into contact with these Teflon-coated skirt panels. If such contacts did occur, the rough edges of the top and riser portions or the step of the steel tongs of a hand truck may scrape and gorge out portions of the Teflon coating, leaving a rough textured surface similar to that of a Teflon-coated frying pan which has been scraped and gouged. Such a rough textured skirt panel is not allowed by safety code requirements in this country, as discussed above. Thus, while the use of such Teflon-coated skirt panels would appear to be a desirable safety feature in new escalators, such coated panels could not be used on old escalators in which the steps can be shifted laterally by movement of the passengers on the escalator so as to rub against the skirt panels.
The benefits of using escalator skirt panels which are coated with a low friction material, such as Teflon, have been known for many years by escalator manufacturers in this country. For example, U.S. Pat. No. 3,144,118, insured Aug. 11, 1964 to Andrew Fabula, and assigned to Otis Elevator Company, describes such Teflon-coated escalator skirt panels and their advantages. However, the use of such Teflon-coated skirt panels has not been adapted by any major escalator manufacturer in this country, perhaps for the reasons discussed above. The skirt panels of all escalators manufactured in this country have a hard smooth surface, such as stainless steel or porcelain enamel, which is resistant to scratching and is easy to clean.
The Hitachi Company also recommends that an adhesion-preventing spray be applied to escalator panels to reduce friction between an object on the moving step which is pressed against the panel, as discussed above. However, to be effective, such a procedure requires constant, careful maintenance and, to a certain extent, well-mannered passengers. For example, children sometimes intentionally put their rubber soles on the tread or riser sides of escalator steps to rub them against the adjacent skirt panel to hear the screeching noise they create. If there is little or no noise, they exert more pressure to cause such noise, thereby removing the layer of wet lubricant. Even if such an action by a child does not result in his shoe becoming entrapped in the running clearance gap in the step and the skirt panel, it will have wiped away much of the lubricant, and thus reduce the protection against entrapment afforded by this lubricant to a subsequent passenger.
In many escalator locations, such as office buildings or department stores, cleaning personnel regularly (often nightly) apply spray cleaning agents and wipe down with rags, finger marks on balastrades and the scuff marks on skirt panels, thus removing adhesion-preventing sprays (usually applied by escalator maintenance mechanics) from the exposed portion of the skirt panel.
In other escalators locations, such as subway stations, or sport stadiums, where the escalator skirt panels are seldom cleaned, the wet adhesion-preventing spray applied to the skirt panels attracts dirt, dust and lint. Unless such panels are thoroughly cleaned and lubricant reapplied at regular intervals, such dirt and dust attracted to the lubricant can cause it to become gummy and sticky, causing the panel coefficient of friction to increase to a value greater than that of a bare, unlubricated panel.
Each escalator step is positioned and guided by a pair of step roller wheels, which are disposed on each side of the step for rotation about a horizontal axis, approximately 13 inches below the face of the step tread, and by a pair of chain wheels which are also disposed on each side of the step and which are rotatable about a horizontal axis of the step approximately 8 inches below the face of the step tread and approximately 4 inches outboard of the step edges. The step wheels and the chain wheels ride in two separate track systems. The chain wheels are incorporated in respective continuous step roller chains, which are engaged and driven by respective drive machine sprockets to move the escalator steps along a path of travel determined by the two track systems.
The step wheel and chain wheel tracks along the inclined portion of the step travel include bottom tracking surfaces over which the wheels roll, which determine the desired longitudinal and vertical movement of the steps, and vertically-extending side tracking surfaces which are spaced from the inner or outer sides of the wheels to provide sufficient clearance for the wheels to freely rotate without binding, and which thus determine the maximum lateral movement of the steps from a desired center line position. Thus, it is seen that some lateral movement of the stair must be allowed, even on newly installed escalators, to prevent binding of the step or chain wheels within their respective tracks. Therefrom, the skirt panel between which the steps run must be positioned so that the running clearance gap between each skirt panel and the sides of the steps is sufficient to allow for the side motion of the steps, so that the side of the moving step will not engage either skirt panel during operation of the escalator.
Thus, one way of reducing the possibility of objects getting caught between the sides of the steps and the skirt panels is to provide a lateral guidance system for the steps to reduce the side motion of the steps and thus reduce the operating clearance required between the stationary skirt panels and the moving steps. One such lateral guidance system for escalator steps is described in U.S. Pat. No. 2,813,613, issued Nov. 19, 1957 to S. G. Margles, and assigned to the Otis Elevator Company. In this system, each step includes two horizontally-extending castors typically fastened to the frame of each step, one on each side of the step. Each castor includes a hard rubber wheel which extends slightly beyond the edges of the step tread plate and riser, in rolling contact with the adjacent skirt panel. In this way, the two skirt panels serve as a guide track for the castor rollers of each step, to thus maintain a constant uniform clearance between each side of the step and the adjacent skirt panel throughout the step travel. In this system, the peripheral area of each castor wheel in contact with one of the skirt panels is relatively small; thus, the unit pressure applied to the castor wheel as a result of an eccentric load on the escalator step may be relatively high, causing rapid wear on the castor wheel and the wheel bearing. Also, since the axis of rotation of the castor is offset from the axis of rotation of the castor wheel, axial loads applied to the castor wheel produce an eccentric load on the castor shank bearing. Thus, in order to maintain this lateral guide system in good operating condition, it may be necessary to regularly replace not only the castor wheel, but also the castor wheel bearings and the castor shank bearings. This lateral guide system has never been used on production escalators manufactured in this country, perhaps because of the increased maintenance expense required.
In the escalator step described in U.S. Pat. No. 2,981,397, issued Apr. 25, 1961 to Hans E. Hansen, and assigned to Westinghouse Electric Corporation, the tread cleats immediately adjacent each stairway skirt panel are fabricated of resilient material such as rubber, having a higher coefficient of friction than that of a adjacent stairway parts, which are fabricated of a substantially non-resilient material such as aluminum. When an object such as a passenger's shoe comes into contact with the resilient cleat and the adjacent skirt panel, the force exerted on the top of the resilient cleat by this object will cause the cleat to move in a direction such that the gap between the flexible cleat and the adjacent skirt panel will be closed, thus preventing this object from being drawn into the gap by the skirt panel as the stairway moves in an upward direction. In order for this protective device to function properly, the force must be applied by the object to the top of the flexible tread before the object is drawn into this gap. Thus, this flexible cleat offers no protection to a youngster who presses the toe of his sneaker or his fingers against the skirt panel without contacting the flexible cleat. In such a case, his finger or toe may be drawn into this gap by the skirt panel before any pressure is applied to the top of the flexible cleat. In such a case, the use of such a flexible cleat can increase the danger to the child, since the trapped finger or toe will exert a force on the side of the flexible cleat to deflect this cleat inwardly and widen the gap. It is perhaps for this reason that this flexible cleat arrangement has been seldom, if ever, used on commercial escalators in this country.
U.S. Pat. No. 3,986,595, issued Oct. 19, 1976, to Asano et al, and assigned to the Mitsubishi Company of Japan, describes a safety device, which is disposed at either the tread or riser edges of a step adjacent one of the skirt panels, for reducing the gap between the escalator step and the skirt panel after an object has become entrapped there between, at a point inward of the entrapped object, to thus prevent the object from being pulled inwardly by the skirt panel beyond this point at which the gap has been narrowed. On upward moving escalators, the device includes a sensor element and a displacement element which are mounted to, and extend along the side of the step tread. The sensor element is slidably mounted to the step so that it is vertically displacable relative to the step. The top side of the sensor element serves as the outermost cleat of the step tread, and is normally higher than the fixed cleats of the step tread. The sensor element has a lower beveled edge which is tapered inwardly and rests against a complimentary, outwardly-tapered, beveled edge of a displacement element, which is coextensive with the sensor element along the side of the step tread. The displacement element is pivotally attached to the step at its lower portion, and is resiliently biased so that normally the flat outer surfaces of the sensor element and the displacement element are coplanar and parallel to the adjacent skirt panel, to thus define a uniform gap between the step and the skirt panel. When an object such as the toe of a sneaker or the finger of a child is pressed against the skirt panel during upward movement of the escalator steps and is drawn by the skirt panel into the gap between the sensor element and the skirt panel, the force applied by the object on the sensor element causes the sensor element to be displaced downwardly. This downward displacement of the sensor element causes the upper beveled side of the displacement element to rotate outwardly, reducing the gap between the displacement element and the skirt panel and preventing the entrapped object from being drawn between the displacement element and the skirt panel. On downward moving escalators, the sensor element and displacement element can be disposed along the riser side of the step to limit the entrapment of any object which is drawn by the skirt panel into the gap between the sensor element defining the edge of the step riser and the skirt panel.
One disadvantage of these two safety devices is that they are mutually exclusive devices, that is, only one or the other of these two devices can be used on any one escalator step. Thus, on an escalator equipped with one or the other of these devices, the devices perform their intended safety function when the escalator is moved in one direction, but are ineffective when the escalator is moved in the opposite direction. Also, for certain objects, these devices could operate to increase the difficulty of disengaging the object. For example, if a woman trips or faints and her hair is drawn into the gap between the displacement element and the skirt panel before the sensor element has be displaced downward, the subsequent displacement of this sensor element by the woman's head, which is pulled downward by the entrapped hair against the sensor element, and the resulting outward movement of the displacement element, may prevent, or at least make more difficult, the release of the entrapped hair.
U.S. Pat. No. 4,236,623, issued Dec. 2, 1980, to Duane B. Ackert, discloses inclined guide strips which are mounted to the two sides of an escalator step tread, respectively. Each guide strip extends the full longitudinal length of the step tread. Each guide strip has a flat top portion and a beveled ramp portion which slopes upwardly and laterally outwardly from the extreme inner edge of the guide strip to the top flat surface. Each guide strip is fabricated of a material such as urethane which is relatively smooth and slippery for minimum friction, has a minimum tendency to adhere soft, hot and sticky articles, and is somewhat brittle so that it will readily break in the event of a jam. The inclined portion of each guide strip functions to guide articles that are close to the edge of the step tread away from such edge. The low coefficient of friction of the guide strip material and the slope or inclination of its ramp portion creates a tendency for such articles to slide downwardly away from the edge of the step. The vertical outer side wall of each guide strip extends outwardly beyond the side of the step to which it is mounted, so that the width of the running clearance gap between the two stationary strip panels and respective sides of the moving step is determined by the two guide strips. If the lateral displacement of the step increases due to wear of various moving elements of the escalator, so that the outer side wall of the guide strip comes into contact with the adjacent strip panel, the softness of the guide strip material prevents any scratching of the skirt panel. However, when the various elements of escalator become worn enough so that the sudden shift of a passenger standing on the step causes a sudden lateral movement of the step, the fact that the material of the guide strip is somewhat brittle can be disadvantageous, in that the strip may break when the step is abruptly shifted against the adjacent skirt panel. Also, since the preferred height of the outer side wall of the guide strip is only about 1/4" so that if the step is eccentrically loaded so as to hold the outer side wall of the guide strip in contact with the skirt panel, the pressure per unit area may be relatively high, resulting in rapid wear of the outer side wall of the guide strip and thus causing an increase in the normal running clearance gap determined by this outer side wall.
The above-described known methods and devices for minimizing the occurrence of entrapment accidents on escalators all presume that it is necessary to prevent contact between the two stationary skirt panels and the escalator steps moving therebetween, and therefore, that a running clearance gap between each moving step side and the adjacent stationary skirt panel is a necessary, albeit undesirable, feature of all escalators. Thus, it would be highly desirable if new escalators could be designed, and existing operating escalators modified, so that not only would contact between the skirt panels and the escalator steps be non-harmful, but also that such contact would contribute to the smooth operation of the escalator and reduce wear and consequent maintenance on other elements of the escalator. In such a case, a minimum running clearance gap between each moving step side and the adjacent stationary skirt panel would not only be unnecessary, but also undesirable. Thus, this gap, and the danger of entrapment posed by this gap, could be eliminated.